Bill Ewing, race operations manager for the Lansing Marathon, said the flood warning for the Red Cedar River prompted the changes.

Originally, race organizers had planned to utilize about 7 miles of the River Trail as part of a 13.1 mile half-marathon course; full marathon racers would run the loop twice.

“Unfortunately, low lying areas are either currently underwater or will be underwater as the river reaches its flood stage,” Ewing said.

But some low-lying portions of the River Trail are already underwater, Ewing said, and others are expected to be flooded by Sunday, April 21, when the half- and full marathons are run.

To cope, organizers are implementing a pre-designed contingency plan, which includes shifting the race from the flooded trails onto nearby streets.

Organizers had a contingency course designed and ready to implement, Ewing said, and are in the process of doing so.

The basic layout of the course will remain the same, with marathoners running the half-marathon course twice; the start and finish will be unchanged.

Officials will continue to monitor the conditions along the changes route until the race begins, making any changes necessary to preserve the safety of runners, Ewing said.

At the same time, officials are working overtime to ensure the alternate race course is certified as a Boston Marathon qualifier, meaning runners who finish under certain time thresholds will be permitted to run the prestigious race next year.

The rain is just the most recent curveball thrown organizers’ way.

In the wake of the bombings at the Boston Marathon, city officials, race organizers and the Lansing Police Department are ramping up security for the weekend of races.

“Security is on everybody’s mind; we’re still working to redeploy our resources and working with Lansing city services -- police, fire, emergency, medical, -- to provide the safest environment for spectators and runners,” Ewing said.

Race officials encourage anyone who’d like to volunteer to visit the race website, Lansing Marathon.com, for more information.